1. Field of the Invention
The invention relates to an electrochemical storage cell of the alkali metal and chalcogen type with at least one anode space for receiving the anolyte, and one cathode space for receiving the catholyte, which are separated from each other by an alkali ion-conducting solid electrolyte and are bounded, at least in some places, by a metallic housing.
2. Description of the Prior Art
Such rechargeable electrochemical storage cells with a solid electrolyte are highly suited for constructing storage batteries with high energy and power density. The solid electrolytes used in the alkali-chalcogen storage cells use solid electrolytes, made for instance of .beta.-aluminum oxide, which are distinguished by the fact that the partial conductivity of the mobile ions is very high and the partial conductivity of the electrons is several powers of ten smaller. By using such solid electrolytes for constructing electrochemical storage cells practically no self-discharge takes place since the electron conductivity is negligible and the reaction substances cannot get through the solid electrolyte as neutral particles.
A specific example for such rechargeable electrochemical storage cells are those of the sodium and sulfur type, the solid electrolyte of which is made of .beta.-aluminum oxide. It is an advantage of this electrochemical storage cell that no secondary electrochemical reactions occur during the charging. The reason for this is again that only one kind of ions can get through the solid electrolyte. The current yield of such a sodium-sulfur storage cell is, therefore, near 100%. In these electrochemical storage cells, the ratio of energy content to the total weight of such a storage cell is very high as compared to lead storage batteries, because the reaction substances are light and much energy is released in the electrochemical reaction.
The electrochemical storage cells of this design, however, have the disadvantage that the solid electrolyte can break if too high a voltage is applied to the storage cells. Aging or mechanical damage of the solid electrolyte can also lead to their fracture. As a consequence, sodium and sulfur flow together and react directly with each other. This results in a large temperature rise of the storage cell, so that in the worst case the destruction of the cell housing or an explosion can come about.
From German Published Non-Prosecuted Application DE-OS No. 25 51 604, an electrochemical storage cell is known which is provided with a safety insert which is supposed to prevent the confluence of sodium and sulfur. This safety insert has the disadvantage that the solid electrolyte can have only a simple geometry, and also must be designed as a tube closed on one side. This limits the power density of the storage cell. Since such a safety insert must practically have the same area as the solid electrolyte, the weight contribution of the safety insert is no longer negligible as compared to the total of weight of the storage cell, which again diminished the power density and the energy density of such a storage cell.